In the proposed study an animal model will be provided which allows for observation of most aspects of carcinogenesis directly upon large bowel tissue of hamsters. The specific aims are: 1. To isograft hamster large bowel tissue to the cheek pouches of BIO (R) 15, 16 inbred Syrian hamsters to be highly receptive to isogeneic as well as allogeneic and xenogeneic tissue grafts. The methods of procedure are essentially modifications and extensions of those described by Kendrick, Nettesheim and Hammons, who introduced a new experimental model for respiratory carcinogenesis studies, namely, tumor induction in tracheal grafts, and by Handler. 2. To produce pathogenic changes leading to carcinomas in these transplants by inoculation of pellet implantation of polycyclic hydrocarbons, etc. 3. To directly observe microscopical in vivo alterations in the morphology of certain foci. 4. To confirm the in vivo changes by adequate histopathologic study. 5. To obtain serially transplantable large bowel tumors following induction in hamsters.